Method of injection fluid monitoring

ABSTRACT

A method of monitoring an injection substance injected into an injection well penetrating the earth and a method of monitoring an underground reservoir storing a substance introduced through an injection well are described. The methods include disposing a monitoring system in a borehole, both a transmitting and a first receiving portion of the monitoring system being disposed in the borehole. The method of monitoring an injection substance also includes injecting the injection substance into the injection well, and monitoring, using a processor processing the received signal, flow of the injection substance out of the injection well. The method of monitoring an underground reservoir includes injecting the injection substance into the injection well for storage in the underground reservoir, and monitoring, using a processor processing the received signal, boundary conditions surrounding the underground reservoir.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Non-Provisional Application of U.S. ProvisionalApplication No. 61/746,180 filed Dec. 27, 2012, the disclosure of whichis incorporated by reference herein in its entirety.

BACKGROUND

Injection wells are used for various purposes in the drilling industry.As one example, injection fluid (e.g., water, CO₂) may be injectedthrough the injection well toward a producing well (producing oil, forexample) to increase pressure and thereby encourage production. However,once the injection fluid front reaches the production well such that theinjection fluid is being produced, the production well is no longerviable. Prior systems to monitor injection fluid have been disposed inthe production well or one or more monitor wells (separate from theproduction well and injection well) or some combination thereof. Thesystems obtain resistivity or conductivity (inversely proportional toresistivity) measurements around the borehole in which they are locatedand can determine the boundary between materials that have discerniblydifferent resistivity values (e.g., the boundary between a productionfluid like oil and an injection fluid like water). When such a system islocated in the production well or in a monitor well in the vicinity ofthe production well, it indicates when the fluid front from theinjection well has reached or nearly reached the production well.However, the information is not timely enough to control the injectionprocess to potentially prolong the use of the production well. Priormethods of monitoring are also problematic because the injected fluidmay not necessarily reach the production well due to heterogeneityand/or permeability anisotropy around the injection well. In this case,the direction and flow rate from the injection well is unknown. Anotherexemplary purpose of an injection well is for the introduction ofmaterial into an underground storage reservoir. In this case, the sealon the storage reservoir must be monitored to ensure that the storedmaterial is not leaking into the surrounding area.

SUMMARY

According to an aspect of the invention, a method of monitoring aninjection substance injected into an injection well penetrating theearth includes disposing a monitoring system in a borehole, both atransmitting and a receiving portion of the monitoring system beingdisposed in the borehole; injecting the injection substance into theinjection well; and monitoring, using a processor processing thereceived signal, flow of the injection substance out of the injectionwell.

According to another aspect of the invention, a method of monitoring anunderground reservoir storing a substance introduced through aninjection well includes disposing a monitoring system in a borehole,both a transmitting portion and a receiving portion of the monitoringsystem being disposed in the borehole; injecting the injection substanceinto the injection well for storage in the underground reservoir; andmonitoring, using a processor processing the received signal, boundaryconditions surrounding the underground reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several Figures:

FIG. 1 illustrates a cross-sectional view of an injection substancemonitoring system according to an embodiment of the invention;

FIG. 2 illustrates a cross-sectional view of an injection substancemonitoring system according to another embodiment of the invention

FIG. 3 depicts the monitoring system in the injection well according toan embodiment of the invention;

FIG. 4 depicts the monitoring system in the injection well and a monitorwell according to an embodiment of the invention;

FIG. 5 depicts the monitoring system in the injection well and a monitorwell according to another embodiment of the invention

FIG. 6 depicts the monitoring system according to an embodiment of theinvention

FIG. 7 illustrates a cross-sectional view of a monitoring systemaccording to an embodiment of the invention;

FIG. 8 illustrates a cross-sectional view of an injection substancemonitoring system according to an embodiment of the invention; and

FIG. 9 is a flow diagram of a method of monitoring an injection fluidaccording to an embodiment of the invention.

DETAILED DESCRIPTION

As noted above, prior injection monitoring systems have been positionedin the production well or in monitor wells near the production well. Anexemplary injection arrangement positions a number of injection wellssurrounding the production well. The injections wells may even beessentially equidistant from the production well, and each injector mayeven inject the injection fluid at the same rate. However, inhomogeneityin the reservoir may render the injection system inhomogeneous(injection fluid from each injection well reaches the production well ata different time or not at all). For example, the injection fluid frontfrom a given injection well may be advancing toward the production wellfaster than the injection fluid front from any of the other wells. Ifthis were determined early in the injection process, the given injectionwell may be choked off to increase the time until an injection fluidfront reaches (and contaminates) the production well. However, amonitoring system in the production well would not be capable of makingsuch a determination in time to prolong the production. This is becausethe system in the production well would only identify the injectionfluid front when it has already approached the production well. Also, ifone of the other injection wells' injection fluid had been misdirectedaway from the production well due to the permeability anisotropy aroundthat injection well, the production well would not detect that fluidfront over a length of time but would not provide any information aboutthe directivity of that injection fluid.

Embodiments detailed herein describe a method of monitoring boundaryconditions from the injection well itself. By detecting the boundarybetween the material injected through the injection well and surroundingmaterial, the fluid front advancing toward a production well (or in anunintended direction other than the direction of the production well) ormaterial injected into a storage reservoir may be effectively monitoredduring its travel into the reservoir and throughout the useful life ofthe reservoir.

FIG. 1 illustrates a cross-sectional view of an injection substance 101monitoring system 130 according to an embodiment of the invention. Whileany system that resides within a single injection well and monitorsboundary conditions from that injection well may be used, a transientelectromagnetic (EM) system including a transmitter 110 and one or morereceivers 120 pair in the injection well 100 is discussed as anexemplary monitoring system 130 in the embodiment discussed withreference to FIG. 1 and is detailed with reference to FIG. 2. Theproduction well 150 is shown as another borehole penetrating the earth160 in an area including a formation 165, which represents anysubsurface material of interest in the production. A computer processingsystem 140 may process the data obtained by the monitoring system 130.The processing may include taking resistivity measurements and findingthe fluid boundary, if any, based on the received conductivity. Inalternate embodiments, downhole electronics 145 that are part of adownhole tool 105 may execute the processing. FIG. 2 illustrates across-sectional view of an injection substance 101 monitoring system 130according to another embodiment of the invention. FIG. 2 shows ahorizontal production well 150 and a horizontal injection well 100. Allof the embodiments of the monitoring system 130 discussed herein applyto both vertical wells (see e.g., FIG. 1) and horizontal wells.

FIG. 3 depicts the monitoring system 130 in the injection well 100according to an embodiment of the invention. As noted above, theexemplary transient EM monitoring system 130 is one embodiment of asystem that may be used, but any system that facilitates the monitoringof fluid boundary dynamics from the injection well 100 may be used toimplement embodiments of the method and system described herein. Forexample, a continuous-wave system rather than a transient EM system maybe used as the monitoring system 130. The transmitter 110 may be a threecomponent transmitter with antennas oriented in the z, x, and ydirections. These directions are parallel to the longitudinal axis ofthe injection well 100, orthogonal to the longitudinal axis and orientedtoward the production well 150, and orthogonal to the longitudinal axisand transverse to the production well 150, respectively. An array ofreceivers 120 a-120 n may be disposed in the injection well 100. Each ofthe receivers 120 may be a three component receiver with antennasoriented in the x, y, and z directions. The transmitter 110 and one ormore receivers 120 may be moved along the length of the injection well100 and may provide information as a function of depth. In otherembodiments, the transmitter 110 and one or more receivers 120 may beaffixed to a particular position within the injection well 100. In stillother embodiments, a number of sets of transmitters 110 and receivers120 may be positioned and may even be affixed along the length of theinjection well 100. FIG. 4 depicts the monitoring system 130 in theinjection well 100 and a monitor well 410 according to an embodiment ofthe invention. According to the alternate embodiment shown in FIG. 4,some of the array of receivers 120 b-120 n, are disposed in a monitorwell 410 while the transmitter 110 and one receiver 120 a (or more) aredisposed in the injection well 100. FIG. 5 depicts the monitoring system130 in the injection well 100 and a monitor well 510 according toanother embodiment of the invention. According to the alternateembodiment shown in FIG. 5, one or more receivers 120 may be in amonitor well 510 while the transmitter 110 is disposed in the injectionwell 100. In a transient EM monitoring system 130, this separation ofthe transmitter 110 and one or more receivers 120 is possible whensynchronization of the transmitter 110 and receiver(s) 120 is included.The synchronization (to within a few microseconds) may be achieved, forexample, via hardwire or fiber optic connection between the transmitter110 and receiver(s) 120. In alternate embodiment, wirelesssynchronization of the transmitter 110 and receiver(s) 120 may beperformed.

While each of the various types of transmitter/receiver systems that maybe used as the monitoring system 130 may have individual strengths, theexemplary transient EM monitoring system 130 addresses two concerns.First, transient (time-domain) measurements relative to continuous-wavemeasurements provide improved spatial resolution. Second,signal-to-noise ratio is improved by increasing the strength of thetransmitter and receiver magnetic dipoles. The transmitter 110 andreceiver 120 of the present embodiment are designed to generate arelatively large switchable dipole (e.g., dipole moment of 1 kAm²) withpower consumption that is more than a hundred times less than with aconventional long-coil. The monitoring system 130 measures conductivity.The monitoring system 130 operates by altering the transmittedelectromagnetic (EM) field to produce a transient EM signal. Thereceiver 120 receives a signal based on the transient EM signaltransmitted by the transmitter 110. This received signal represents theconductivity of the surrounding material.

By detecting a transition in conductivity of that surrounding material,the fluid front of the injection substance 101 may be detected and itsdirectivity and speed may be monitored. The directivity of the injectionsubstance 101 is based on the permeability anisotropy around theinjection well 100. That is, the injection substance 101 will not flowin all directions uniformly from the injection well 100 and, as notedabove, may not reach a targeted production well 150 at all within agiven period of time. By monitoring the flow of the injection substance101, the permeability anisotropy around the injection well 100 may bedetermined. Because the exemplary monitoring system 130 (transient EM)measures conductivity, an injection substance 101 that has a lowerconductivity than that of surrounding material (e.g., oil around aproduction well 150) may be monitored for a longer distance away fromthe injection well 100 than an injection substance 101 with a higherconductivity than that of surrounding material. For example, CO₂ has alower conductivity than oil. Thus, when CO₂ is the injection substance101 injected into the injection well 100, it may be monitored as itadvances toward the oil for a greater distance than if water (with ahigher conductivity than oil) were used as the injection substance 101.

FIG. 6 depicts the monitoring system 130 according to an embodiment ofthe invention. The transient EM monitoring system 130 is again used asan example. In the embodiment shown in FIG. 6, the borehole 330 (e.g.,injection well 100 or monitor borehole 410, FIG. 4 810, FIG. 8) includesa casing 310. In this case, especially if the casing is conductive(e.g., steel), the magnetic flux going through the casing 610 may resultin the production of eddy currents. Thus, in the embodiment shown inFIG. 6, a magnetically permeable or ferrite material 620 surrounds thecasing 610. The lower impedance path created by the magneticallypermeable or ferrite material 620 reduces the magnetic flux through thecasing 610. In this case, the transient EM monitoring system 130 ismounted outside the casing 610 and outside the magnetically permeable orferrite material 620.

FIG. 7 illustrates a cross-sectional view of a monitoring system 130according to an embodiment of the invention. In the embodiment shown inFIG. 7, an injection substance 101 is injected into the injection well100 for storage in an underground reservoir 710. The injection substance101 may be carbon dioxide, waste water, or natural gas, for example. Byusing the monitoring system 130, the fluid front of the injectionsubstance 101 into the reservoir 710 as well as any leak from thereservoir 710 may be monitored.

FIG. 8 illustrates a cross-sectional view of an injection substance 101monitoring system 130 according to an embodiment of the invention. Themonitoring system 130 according to the present embodiment resides in amonitor borehole 810 in proximity to the injection well 100. Forexample, if the distance D from the injection well 100 to the productionwell 150 is 100 feet, the distance d from the injection well 100 to themonitor borehole 810 may be approximately 5 to approximately 10 feet.Because the monitor borehole 810 includes the monitoring system 130 tomonitor the injection substance 101 from the injection well 100 (ratherthan a fluid front approaching the production well 150) and because themonitor borehole 810 is proximate to the injection well 100, a singlemonitor borehole 810 is sufficient though two or more monitor boreholes810 may be used. All of the features discussed with reference to themonitoring system 130 in the injection well 100 above apply, as well, tothe monitoring system 130 in the monitor borehole 810. For example, themonitor borehole 810 may include a casing 610 and a permeable or ferritematerial 620 (FIG. 6). The monitoring system 130 in the monitor borehole810 may be a continuous-wave system rather than a transient EM system.The monitor borehole 810 may be used to monitor injection substance 101intended to encourage production in the production well 150 and tomonitor injection substance 101 stored in an underground reservoir 710(FIG. 7).

FIG. 9 is a flow diagram of a method 900 of monitoring an injectionsubstance according to an embodiment of the invention. The method 900according to the exemplary embodiment described herein uses thetransient EM monitoring system 130 described with reference to FIG. 2.The method 900 includes inserting a monitoring system 130 transmitter110 and one or more receivers 120 into the injection well 100 (block910). At block 920, the method 900 includes injecting the injectionsubstance 101 into the injection well 100. At block 930, the method 900includes altering the transmitted EM field to produce a transient EMsignal out of the injection well 100. At block 940, receiving a receivedsignal based on the transient EM signal facilitates determiningconductivity. Monitoring the injection substance 101 based on thereceived signal (block 950) includes monitoring the fluid front based ona difference in conductivity between the injection substance 101 and thesurrounding material. This monitoring may include the use of time-lapsemeasurements to determine the motion of the injection fluid front. Thismonitoring may include monitoring injection fluid directed to aproduction well 150 to increase production. The monitoring may alsoinclude monitoring a substance injected into an underground reservoir710 (FIG. 7).

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

1. A method of monitoring an injection substance injected into aninjection well penetrating the earth, the method comprising: disposing amonitoring system in a borehole, both a transmitting and a firstreceiving portion of the monitoring system being disposed in theborehole; injecting the injection substance into the injection well; andmonitoring, using a processor processing the received signal, flow ofthe injection substance out of the injection well.
 2. The methodaccording to claim 1, wherein the disposing the monitoring system in theborehole is in the injection well.
 3. The method according to claim 2,further comprising disposing a second receiving portion of themonitoring system including one or more receivers in the injection well.4. The method according to claim 2, further comprising disposing asecond receiving portion of the monitoring system including one or morereceivers in a monitor well proximate to the injection well.
 5. Themethod according to claim 1, wherein the disposing the monitoring systemin the borehole is in a monitor borehole proximate to the injectionwell.
 6. The method according to claim 1, wherein the disposing themonitoring system in the borehole includes disposing at least oneelectromagnetic (EM) transmitter in the borehole, altering, using acontroller coupled to the at least one EM transmitter, the transmittedEM field to produce a transient EM signal, and receiving, using one ormore receivers disposed in the borehole, a received signal based on thetransient EM signal.
 7. The method according to claim 6, furthercomprising determining conductivity based on the received signal.
 8. Themethod according to claim 7, wherein the monitoring includes identifyinga boundary between the injection substance and another substance basedon the conductivity.
 9. The method according to claim 1, wherein themonitoring includes monitoring a direction of the flow.
 10. The methodaccording to claim 9, wherein the monitoring the direction of the flowincludes determining permeability anisotropy of formation surroundingthe injection well.
 11. The method according to claim 1, wherein thetransmitting portion and the receiving portion of the monitoring systemmove along a length of the borehole and the monitoring is performed atdifferent depths.
 12. The method according to claim 1, wherein aplurality of the monitoring systems are disposed along a length of theborehole.
 13. The method according to claim 1, further comprisingdisposing a casing in the borehole and a magnetically permeable materialsurrounding the casing, wherein the disposing the monitoring system isbetween the magnetically permeable material and the borehole wall.
 14. Amethod of monitoring an underground reservoir storing a substanceintroduced through an injection well, the method comprising: disposing amonitoring system in a borehole, both a transmitting portion and a firstreceiving portion of the monitoring system being disposed in theborehole; injecting the injection substance into the injection well forstorage in the underground reservoir; and monitoring, using a processorprocessing the received signal, boundary conditions surrounding theunderground reservoir.
 15. The method according to claim 14, wherein thedisposing the monitoring system in the borehole is disposing themonitoring system in the injection well.
 16. The method according toclaim 15, further comprising disposing a second receiving portion of themonitoring system including one or more receivers in the injection well.17. The method according to claim 15, further comprising disposing asecond receiving portion of the monitoring system including one or morereceivers in a monitor well proximate to the injection well.
 18. Themethod according to claim 14, wherein the disposing the monitoringsystem in the borehole is disposing the monitoring system in a monitorborehole proximate to the injection well.
 19. The method according toclaim 14, wherein the disposing the monitoring system includes disposingat least one electromagnetic (EM) transmitter in the borehole, altering,using a controller coupled to the at least one EM transmitter, thetransmitted EM field to produce a transient EM signal, and receiving,using one or more receivers disposed in the borehole, a received signalbased on the transient EM signal.
 20. The method according to claim 14,further comprising determining conductivity based on the receivedsignal, wherein the monitoring includes identifying a boundary betweenthe substance and another substance surrounding the undergroundreservoir based on the conductivity.
 21. The method according to claim14, wherein the monitoring includes detecting a leak in a seal of theunderground reservoir based on a flow of the substance out of theunderground reservoir.
 22. The method according to claim 14, wherein thetransmitting portion and the receiving portion of the monitoring systemmove along a length of the borehole and the monitoring is performed atdifferent depths.
 23. The method according to claim 14, wherein aplurality of the monitoring systems are disposed along a length of theborehole.
 24. The method according to claim 14, further comprisingdisposing a casing in the borehole and a magnetically permeable materialsurrounding the casing, wherein the disposing the monitoring system isbetween the magnetically permeable material and the borehole wall.
 25. Amethod of monitoring an injection substance injected into an injectionwell penetrating the earth, the method comprising: disposing atransmitting portion of a monitoring system in a first borehole;disposing a receiving portion of the monitoring system in a secondborehole; synchronizing the transmitting portion and the receivingportion time; injecting the injection substance into the injection well;and monitoring, using a processor processing the received signal, flowof the injection substance out of the injection well.